Automatic transmissions (ATs) have been known as means for automatically shifting gears of vehicles. In recent years, a mainstream type of the ATs has a combinational structure of, for instance, a torque converter, a plurality of planet gears and a plurality of clutches. Such a type of AT does not require an operator to perform clutch operations, normally required in manual transmissions (MTs), in starting moving a vehicle, stopping a vehicle and shifting gears due to a continuous gear shifting action by the torque converter and an automatic switching among the plural clutches.
However, torque converters are configured to transmit power through fluid. Therefore, the power transmission efficiency of the ATs is lower than that of the MTs configured to mechanically couple the input side and the output side directly in transmitting torque. Therefore, the ATs have a drawback of degrading fuel consumption of the vehicles although having an advantage of reducing operators' effort.
In view of the above, automated manual transmissions (AMTs), structured based on the MTs, have been proposed for reliably achieving the transmission efficiency of the MTs, and simultaneously, eliminating the need of clutch operations. In the AMTs, the clutch operations of the MTs and the gear-shifting operations of the transmissions are automated. Therefore, the AMTs can reliably achieve a transmission efficiency equivalent to that of the well-known MTs, and simultaneously, eliminate the need of clutch operations.
However, the AMTs are configured to decouple the clutches in performing a gear-shifting operation similarly to the MTs and torque transmission is thereby temporarily prevented. Vehicles travel only by means of inertia force without accelerating while torque transmission is prevented. Such torque transmission prevention greatly affects the acceleration performance of vehicles and tends to make operators feel uncomfortable.
In view of the above, AMTs employing a twin clutch device have been proposed for solving the drawback of the torque transmission prevention (see e.g., Japan Laid-open Patent Application Publication No. JP-A-2002-174262).